Crossbar-switch line-finder system



Oct. 23, 1956 E. J. LEONARD CROSSBAR-SWITCH LINE-FINDER SYSTEMl FiledNov. 12, 1954 3 Sheets-Sheet l Oct. 23, 1956 E. J. LEONARDCROSSBAR-SWITCH LINE-FINDER SYSTEM 3 Sheets-Sheet 2 Filed Nov. l2, 1954Oct. 23, 1956 E. J. LEONARD \-2,768,240

CROssBAR-SWITCH LINE-FINDERSYSTEM Filed NOV. l2, 1954 3 Sheets-Sheet 3TO CONNECTOR -IN RELAYS T0 SW I T0 SW 5 -|N RELAYS TRUNK SWITCH 243 v T05w 5 EON PON FIG. 2, PART 2 United States Patent CROSSBAR-SWITCHLINE-FINDER SYSTEM Edward J. Leonard, Chicago, Ill., assignor toInternational Telephone and Telegraph Corporation, New York, N. Y., acorporation of Maryland Application November 12, 1954, Serial No.468,443

5 Claims. (Cl. 179-18) This invention relates generally to acrossbar-switch line-finder system but is concerned more particularlywith a line-finder system of that type wherein the trunks are givendirect access, as distinct from link access, to the calling lines. Itsprincipal object is to provide a new and improved switchboardarrangement of standardized crossbar switches to comprise separateeconomical finder groups, together with new and improved controllers forthe respective finder groups arranged to avoid false operations whenseparate controllers are associated with respective sections ofsectionalized crossbar switches, or when trunks are connected in commonto two or more iinder groups having separate controllers.

A group of divided, or two-section switches are commonly used to giveaccess to twice as many lines as an equal number of undivided switches.With the usual number of such crossbar switches (such as ten) mounted ona frame, the total number of lines is more than many authorities deemshould be served by a single common controller. Moreover, the number ofswitches involved may be such that the most desirable number of linesserved by one controller cannot be assigned thereto without dividing thelines served by at least one switch into two controller groups, whichhas not heretofore been considered feasible because a switch has but oneset of selecting apparatus and cannot, therefore, be set in but oneselecting position at a time.

Further, it is common practice to suitably multiple the trunks serving aframe of nder switches among the several switches according to thetraffic load and irrespective of the controller groups. Thus, when themost desirable multipling arrangement is used, two or more controllersmay simultaneously test and thereafter select the same idle trunk, whichcannot be tolerated, since it often results in two or more lines beingconnected to the same trunk.

According to the invention, the iirst part of the foregoing problem issolved by arranging that two controllers serving respective sections ofa sectionalized crossbar nder switch have mutually exclusiveinterlocking arrangements which become etfective only when both try atthe same time to control the selecting apparatus of the same switch, andwithout affecting the access of either controller to the non-selectiveparts of the switch which cornprise the sections.

Further, according to the invention, the trunks and the controllers areso arranged and equipped with respect to idle tests of the trunks by thecontrollers that the successful idle testing of a trunk by anycontroller depends upon no other controller attempting at that time totest that trunk.

The abovementioned and other features and objects of this invention andthe manner of attaining them will become more apparent and the inventionitself will be best understood, by reference to the followingdescription of an embodiment of the invention taken in conjunction withthe accompanying drawings comprising Figs. 1 and 2, wherein:

2,768,240 Patented Oct. 23, 1956 Fig. I

Referring now to Fig. l of the drawings, a line-finder frame is shown,comprising switch groups SG1 and SG2. Each such group, serving two -linegroups of lines, is associated with selector or connector frames (notshown) by a common group of trunks 150, comprising trunks -1 to 150-60.The switch groups SG1 and SG2 while being shown arranged side by sidemay be mounted one above the other on a ten-switch frame.

The line-nder frame in response to a calling condition on any line ofthe four groups of lines, functions t0 identify the calling line andassociated switch, selects an idle trunk accessible to such line, andexercises control over the switch groups to extend a connection from thecalling line to the selected trunk.

Switch group SG1, similar to switch group SG2, mounts tive switches SW1to SWS and associated controllers CRI and CRZ. Each of the switches,only the first and last ones of each switch group being shown, issimilar to those disclosed in United States Patent 2,5 77,067 of R. P.Arthur.

In such a switch, it is well-known that severing the horizontal multiplebetween any two adjacent verticals provides two similar groups ofhorizontal multiples with each group having the original number oftermination points and being accessible by a portion of the originalnumber of verticals. The number of verticals having access to eachhorizontal multiple group being determined by the adjacent verticalsselected as the point for severing the horizontal multiple.

In this disclosure, the horizontal multiple of a 25 X20 switch issevered between the twelfth and thirteenth verticals, therebyeffectively providing two 12)(20 sections. In direct-access line-findersystems wherein the lines are terminated on the horizontals and thetrunks are terminated on the verticals, the use of a 25 X20 switch withthe multiple severed as above stated, provides termination points forforty lines and twenty-four trunks, each section serving twenty linesand twelve trunks.

It has been chosen to provide a frame serving four 100-line groups oflines, each group having a common controller. Since the number of lines(40) served by a sectionalized switch is not a multiple of the number oflines (100) in a group, portions of the lines of two separate groupsmust be terminated on the same switch, resulting in two controllers eachcontrolling respective sections of the same switch.

Rather than assigning the lines of a l00-line group to tive sections(each section terminating 20 lines) of three switches, it has beenchosen to assign the lines of one l00line group to the iirst section offive switches, another 100-line group of lines to the second section ofsuch switches, the third group to the rst section of another tiveswitches, and so forth. In this manner, each switch is served by twocontrollers rather than certain switches being so controlled.

As illustrated, the subscriber lines in any switch group are groupedinto ten blocks of twenty lines each and are designated LCIA to LCSB.Therefore, for switch group SG1, comprising iive switches SW1 to SWS,with each switch section serving 20 lines, switch group SG1 serves 200lines, section A of each of the switches terminating 10() lines andsection B terminating another 100 lines.

The originating trunks 150-1 to 150-60 are shown multipled betweenswitch groups and between switch secepeazao tions of the switches ineach group. The disclosed multip'ling arrangement has been chosen forsimplicity in describing the invention, numerous other multiplingschemes being readily applicable. As illustrated, trunk 15th-I over itsbranch 15b-IA is terminated on vetical I of section A of switch 1;branch 15u-IB is terminated on vertical I of section 'B of switch I;branch 1C on Vertical I of section A of switch 6 (switch group SC2); andbranch 1D on vertical I of section Bof switch 6. Trunk 150-2 isterminated on verticals 2 of both sections of switches I and 6; andtrunk 150-60 is terminated on the last vertical of both sections ofswitches and It). In this manner, each trunk is accessible from fourgroups of twenty liners, for a ,cumulative total of eighty lines, andthe four hundred lines (four 100-line groups) of a lineLndervframe haveaccess to sixty different trunks. Other trunking arrangements mayincrease the number of trunks serving each frame or increase the numberof lines accessible to each.

In switch group SGI, being `similar to switch group SG2, two controllersCRI and CR2 are provided for the two v100-line groups of lines.lController CRI is associated with the line circuits LC1A to LCSA of the100 lines terminated on section A of switches I to 5 by conductors incable groups 130 to 53u, and controller ,CR2 is associated with the linevcircuits LCIB to LCSB of the 100 lines terminated on section B of suchswitches by conductors in cable groups 140 to 540.

Controller CRI exercises control over the trunks and hold magnetsassociated with the twelve verticals of section A of switches 1 to 5over respective cable groups 120 to 520, while controller CR2 exercisescontrol over the trunks and hold magnets associated with the twelveverticals'of section B of switches I to 54 over respective cable groups110 to 510.

As hereinbefore noted, since the selecting apparatus (select magnets) ofeach switch are common to both sections A and B, controllers CRI and CR2are interconnected by conductors in cable group l19) to permitoneat-a-time switch association and each are accordingly associated withthe same select magnets control wires of switches 1 to 5 over respectivecablegroups 100 to 569.

From the above, it will be observed that the controllers CRI and CR2separately control their own 100-line groups of lines and theirassociated switch verticals, while both controllers cooperate incontrolling the select magnets of the switches.

In the disclosed multipling arrangement, an originating trunk, such astrunk u-I, is accessible from lines associated with controllers CRI toCR4 and consequently y maybe simultaneously `tested by two or morecontrollers. In order to prevent two lines served by dierentycoutrollers from being connected to the same trunk, Yeachcontrollerincludes a trunk testrelay (not shownin Fig. I) which ismarginal in `operation-so'that in the event the same trunk'is tested bymore than one controller, the resistance of the windings of the'two ormore'test relays in parallel limits the current flow over the testingcircuit, preventing the operation'of any test relay. Upon failure of anytest relay to operate, the associated controllers thereupon test thenext succeeding trunk, the multipling arrangement being such that thenext trunk being tested by one controller is not the same trunk beingtested by another because of randomization. With such testingarrangements in the controllers, it is apparent that any desiredmultipling arrangement may be utilized.

When a line served by section A of switch I of switch group SG1originates a call, the associated line circuit LC1A transmits a tens andunits mark to the associated controller CRI over conductors in cablegroup 130. Controller CRI thereupon identities the switch serving thecalling line, determines thev horizontal (principal and extension)terminating such line, and proceeds to call-in for test the'trunks'accessible thereto, such trunks i being associated withverticals I to I2 of section A of switch 1.

Controller CRI, in response to the tens mark, identities the switchcontaining the calling line and individualizes itself with the tens linegroup containing the calling line. Following such individualization,controller CRI operates the upper or lower auxiliary select magnet or"switch 1 corresponding to the tens group of lines containing the callingline; operates the principal select magnet corresponding to the callingline `in the selected tens group responsive to the units mark; andcalls-in the test conductors of the trunks accessible to such lines andtests them for selection of an idle one.

The test circuit for selecting an idle trunk includes conductors incable group I2@ which are tested simultaneously with the units-markline-identifying operation in order to reduce the testing time of thecontroller.

Responsive to the completion of the auxiliary and principal selectmagnet setting and the testing of the trunks associated Vwith verticalsI to I?. of section A of switch I, controller CRI operates the holdmagnet associated with theselected idle trunk, the operating circuitbeing over conductors in cable group Htl. At such time the calling lineis extended through the Contact bank of section A of switchrI to an idletrunk extending to the selector or connector frame.

Controller CRI, in response to the selector being taken for use, clearsout permitting controller CR2 to become associated therewith in theevent a call in the associated -line group is present.

When .a call is originated in section A of switch I simultaneously withanother call fron-1 a line in section B of switch I, controllers CRI andCR2 both respond to the tens and units marks from their respective linesto identify the line and to extend a connection therefrom to an idletrunk. However, since only one controller can be individualized with asingle switch at any one time, one controller must wait for switchaccess, the controllers being arranged with a fixed order of preferencein favor of controller CRI.

During the time in which controller CRI is individualized with theselecting mechanism of a switch, controller y CR2 responds to the tensand units marks from calling lines in its associated section to identifythe switch serving the calling line, to determine the principal andauxiliary select magnet terminating such line; and to test and select anidle trunk accessible thereto. In this manner, the waiting controllercompletes its line-finding action up to thepoint of switch operation andwhen 'it has access to the selecting mechanism of the switch, theextension of a calling connection is completed with a minimum of delay.

fig. 2

vReferring now to Fig. 2, parts l and 2 of the drawings, the generaloperation of controllerCRI in extending a connection from a callingstation SI on a' calling line LI (terminated on upper horizontal I ofsection A of switch I) to an idle connector or selector will now bedescribed.

The 34 Vrelays (Zhi. to E34) of controller CRI have principal functionsassigned thereto as follows:

Relays 201 to ZI() (tens-group relays) operate to individualize the'calling tens-group of lines with controller CRI and to identify thecalling line switch location as regards to the principal and auxiliaryselect magnets serving such line.

Relay ZII (tens-test) operates in series with the calling tens-grouprelay when the tens-test switch is positioned on such relay;

Relay ZIZ (start) operates responsive to a calling Vcondition appearingon any line in the 100-line group served by controller CRI to start thecontroller into its line nding operation;

Relay 2213 (preference shift) operates on the initiation 0f @ach Call toadvance each of the switches Zei to2@ one step to shift the tens, units,and trunk preference; Relay 214 (time) operates responsive to controllerseizure to control the time which the controller can be individualizedwith one line;

Relay 215 (units-test) operates when the units switch is positioned onthe calling-line units-mark wire, and functions to control the operationof the principal select magnet associated with the calling line;

Relay 216 (select-magnet operate) operates under control of theunits-test relay to transfer the units switch from association with theunits-mark wires to the select magnet operate wires;

Relays 217 to 221 (select-magnet call-in relays) are associated withrespective ve switches and operate to individualize the controller withthe switch serving the calling line to the exclusion of the othercontroller associated with the same switch;

Relay 222 (trunk-test) is marginal in operation and operates responsiveto the trunk switch being positioned on an idle trunk;

Relay 223 (principal oli-normal) is controlled by the trunk-test relayand is operated responsive to an off-normal mark from the principalselect magnet to indicate that the hold magnet associated with theselected trunk may be operated as the selecting operation is complete;

Relays 224 to 228 (idle-test call-in relays) are associated respectivelywith the tive switches and are operated to call-in the idle-testconductors of the trunks associated with the switch section serving thecalling line;

Relay 229 (hold-magnet operate) is controlled by the trunk-test relay toprepare an operate circuit for the hold magnets associated with theselected idle trunk; and

Relays 230 to 234 (hold-magnet call-in relays) are associatedrespectively with the tive switches and are operated to call-in thehold-magnet operate wires associated with the trunks of the switchsection serving the calling line.

Switches 241 to 243 are rotary switches of the wellknown type which areoperated step-by-step in response to stepping pulses generated byinterrupter P240. Tens switch 241 is operated step-by-step intoengagement with the ten (10) tens mark wires of the ten-line groups; theunits switch 242 is operated step-by-step into engagement with the ten(l) units mark wires of the selected tens group; and trunk switch 243 isoperated step-by-step into engagement with the twelve (l2) idle-testwires associated with the trunks accessible to the calling line. Asillustrated, switches 241 and 242 have ten selecting positions whiletrunk switch 243 has twelve selecting positions.

The detailed operation of controller CRI in extending a connection froma calling line L1 to an idle selector SELI by way of its associatedswitch and an idle trunk 150 will now be described.

Responsive to the removal of the receiver (not shown) at station S1 online L1, the usual line loop is closed across the tip and ringconductors T and R. This closed loop is extended through MDF and IDFjumpers to operate line relay I0 of the associated line circuit LCIthrough contacts I and 2 of cutoff relay 12.

Line relay 10, at its contacts I and 2 ground the associated units-markconductor UM1 and the tens-mark conductor TMI. The units-mark conductorUM1 is individual to the calling line while the tens-mark conductor TMIis common to ten lines in the calling ten-line group of lines.

' Ground on the tens-mark wire TMI is extended over the associatedconductor in cable group 130 to the batteryconnected winding ofpreference shift relay 213 through break contacts 12 of the associatedtens group relay 201 and the break contacts 2 of start relay 212.

Preference shift relay 213 operates and at its make contacts 2 and 3extend ground potential to the batteryconnected winding of each of themotor-magnets of switches 241, 242, and 243 causing these switches toadvance their brushes to the next succeeding position. Contacts 1 ofrelay 213 extend ground potential from break contacts 2 of oft-normalrelay 2.23v throughbreak contacts 6 of time relay 214 to thebattery-connected winding of start relay 212.

Start relay 212 operates and at its make contacts 1 extends groundpotential to the battery-connected winding of time relay 214; its breakcontacts 2 open the operate circuit of preference shift relay 213; itsmake contacts 3 prepare an operate circuit for tens-test relay 211; itsmake contacts 4 ground the lock wire L; its make contacts 5 completes aself-locking circuit to normallygrounded release wire RLSE independentof relay 213; and its make contacts 6 extend pulsing ground frominterrupter P240 to the battery-connected winding of the motor magnet oftens switch 241.

Time relay 214 is a slow-operating relay of any type suitable forproviding a delay time of approximately onetenth of a second. After suchperiod of time, relay 214 operates and at its contacts opens the operatecircuit of start relay 212, causing the controller to clear out byremoval of ground from the lock wire L.

Preference shift relay 213 restores and removes ground from the windingof the motor magnet of each of the stepping switches 241 to 243. At suchtime, switch 241 is under control of the interrupter P240 throughcontacts 6 of relay 212.

The ground appearing on the tens-mark conductor TMI is extended to oneside of the winding of the tens-group relay associated with the tensgroup containing the calling line and the other side of each tens-grouprelay is connected to separate positions on the bank of switch 241. Thebrush of tens switch 241, having battery potential from the winding ofthe tens-test relay 211 appearing thereon, advances under control ofinterrupter P240 across the switch bank, successively engaging thetens-mark wires. Assuming the preference shift relay 213 to haveadvanced the brushes of switch 241 to position 1, and the tens-mark wireTMI is grounded, the battery potential appearing on the brush isextended through the winding of the tensgroup relay 201 to the groundappearing on the tens-mark conductor TMI, operating the tens group relay201 and tens-test relay 211 in series.

In the event that the calling line is served by a tenline group otherthan the first, switch 241 advances stepby-step from ground pulsesgenerated by interrupter P240 until the brushes become positioned on agroup relay having the associated tens-mark conductor grounded.

Responsive to the operation of the tirst tens-group relay 201, makecontacts I to 10 extend the units-mark conductors associated with theten lines in the calling tenline group through break contacts of theselect-magnet operate relay 216 to the contact bank of units switch 242;its contacts 11 ground the upper select magnet wire SMU to identify thecalling line as one in the upper tenline groups of lines; its contactsI2 restore relay 213, as noted; and its make contacts I3 ground theswitch wire SW1 to identify the calling line as one served by switch I.

Tens-test relay 211 at its break-make contacts transfers the pulsingground from the motor magnet of tens switch I to the motor magnet ofunits switch 242 and trunk switch 243 causing them to advance theirbrushes step-by-step across the switch bank. At such time switch 241 ispositioned on the tens wire corresponding to the calling ten-line group.

Responsive to the grounding of wire SW1, an operate circuit is extendedto the battery-connected windings of select magnet call-in relay 217,idle-test call-in relay 224, and hold magnet call-in relay 230.

Idle-test call-in relay 224, associated with the idletest wires of thetrunks terminated on the verticals of section A of switch 1, operatesand at its contacts 1 to 12 connect the idle-test wires ITI to IT12 tocorresponding contacts on the switch bank of trunk switch 243 inpreparation for testing operations to select an idle trunk. Contacts 13of relay 224 completes an operate circuit for the hold-magnetcall-in-relay 230.

Hold magnet call-in relay 230, associated with the hold magnet operateswires of the trunk verticals of section 7 Aof switch?.Loperatesand-atits cont-actsV lfto 512, connects the hold magnet wires HMI to HM12 tocorrespondingcontaots 1-to12on relay 229'in preparation for operatingthe 4hold magnet lserving the selectedidle ftrunk.

The Yoperation of select magnet call-in relay 21,7 in response to fthegrounding of wire SW1 `willbe described hereinafter.

'The battery-connected -winding of units-test re1ay 215 is connected tothe brush of units switch 242 and -the battery-connected upper windingof trunk-test ;relay 1222 is Vconnected to the brushof switch 243. Asunits switch 242 and `trunk switch 243 advance lltheirbrushes acrosstheir respective switch banks under control of interrupter P240, the`brush of switch 242 engages the units mark wires UMI to UMli) and thebrush of switch 243 engages fthe idle-,test wire extensions TE1 to'FE1-.2 associated with the twelve trunks served Vby the switchsections.

Responsive tothe engagement of the brush of units switch 242 with theswitch bank contact associated with the units wire UMl, -units wireUB/i1 being grounded responsive to the calling condition on Aline L1,units test relay 215 operates and locks to the ground on lock lead L atits make contacts 3.

Make contacts'l of lunits test relay 215 connect the blush of unitsswitch 242 to the extension ott-normal wire EON `independent of theunits-test relay winding; at its make contacts 2 closes an operatecircuit for selectmagnet operate relay 216; -and at its break contacts 4disconnects the pulsing wire of interrupter P240 from the motor magnetof switch 242, leaving switch 242 positioned in accordance with `thegrounded units mark wire UML Responsive-to the operation of thetens-test relay 211 and .the noted transfer of the pulsing ground fromthe motor magnet of switch 241 to the motor magnet of switch v243, trunkswitch 243 advances its brush stepby-step across its contact bank. Atsuch time, as hereinbefore noted, Vidle-test call-in relay 224 isoperated and the idle-indicating battery potential (resistor 418 ofselector SEL1) or ground potential (make contacts 1 of selector SELl)appearing on the idle-test conductor 1T1, depending upon whether theselector is idle or busy, is extended through the brush and engaged bankcontact of switch 243 and through'break contacts 1 of primary oinormalrelay 223 to the upper winding of trunk-test relay222.

VThe .upper winding of trunk test relay 222 is marginal in that .if atrunk-test relay of another controller is in parallel with relay 222,such condition arising when two controllers Vtest the same trunksimultaneously, the current ow -through the marginal winding is limitedto a non-operate value, and neither of the two test relays operate. Themultipling and grading distribution is randomizedso that in the eventthat two controllers test the sametrunk at the same time and thenadvance to the next position, the testing of the same trunk again willnot ordinarily occur.

Assuming the brush of trunk switch 243 is in engagement with the bankcontact 1 which is associated with trunk branch 156-114, and assumingselector SELL associated with trunk 151 is idle, battery potential fromthe current-limiting resistor 41S of selector SELl appears on theground-connected winding of trunk test relay 222.

Trunk test relay 222 operates and locks operated through its makecontacts 2 to the ground potential appearing on the lock conductor L. Atyits make contacts 1, ytrunk test relay 222 extends the principaloitnormal wire PON to the battery-connected winding of relay 223; and atits break contacts 4 removes the pulsing ground from the motor magnet oftrunk switch 243, stopping it with its brush in associated with theselected idle trunk.

At this point, assuming select magnet call-in relay 217 has .1.191 veroperated, units Sii/19111242 is pQSitiOned 9.1.1

the Yselect magnet-wire corresponding yto Ithe cal1ing=lineandfswitch243 -is lpositioned on lthe hold magnet wire associatedwith -aselected idle trunk. Normally,-ho.wever, select magnet call-in relay 217is operated-simultaneously with Ythe vidle-test call-in relay 224`andselect magnet operation Voccurs coincidentally with the trunkv testoperation just described.

Following the operation of units test -relay 215, selectmagnet operaterelay 216 operates and at its break-make contacts 1 to 10 transfers theswitch -bank wires `from the units-mark wires to the select-magnet wiresSM1 to SM1@l in preparation for operating the select Amagnet serving-the calling line, when the select magnet callin relay operates.

In the event that controller CR2 is idle, .an operate circuit forselect-magnet in relay 217 is complete from battery throughcurrent-limiting resistor 235, .break contacts 16 of relay 217, breakcontacts 16 of the relay-217 in controller CRZ, if such controller isidle, break contacts 17 of relay 217, and the winding of relay 217 tothe ground appearing on wire SW1.

Select magnet call-in relay 217 thereupon operates and at its makecontacts 1 to 10 closes an operate circuit for the principal selectmagnet SM1 to SM10 of the associated switch; at its contacts 11 and 12extends the grounded one ofthe auxiliary select magnet wires SMU and SMLto their associated magnets; at its make contacts 13 and V14 extend theoff-normalwires from the principal magnets SM1 to SM10 and the auxiliarymagnets SMU and YSML to -respective wiresPONV and EON; at its makecontacts 15 locks relay 217 operated independently of controller GRZ;and at its break contacts 15 and 16 removes operating potential from thecall-in relay fof controller -CR2.

The ground from make contacts 11 appearingon wire SMUis thereuponextended ythrough make contacts 1'1 of relay 217 to thebattery-connected winding of the upper select 'magnet'SMU Select magnetSMU operates to select the upper-ten horizontals of switch '1 and at itsoff-normal contacts grounds the extension olf-normal wire EON.

The ground appearing on the extension off-normal wire EONis extendedthrough make contacts 14 of relay 217 to make contacts 1 ofthe unitstest relay 215. Assuming units-test relay 21S is operated and switch 242is Vpositioned in its illustrated position, ground on wire EON isextended to the brush on units switch 242 and over the engaged switchbank contact 1, through contacts 1 of relay 216, and through the.corresponding contact on relay 217 to the battery-connected winding ofprincipal select magnet SM1.

Principal select magnet SM1 operates to Aselect Vthe horizontal in theselected group of ten upper horizontals terminating the calling line,and to close' its oli-normal contacts, grounding the primary off-normalwire PON.

Ground on the off-normal wire PON is vextended through make contacts 13of operated select magnet callin relay 217 to make contacts 1 of thetrunk-test relay 222. At such time, assuming trunk-test relay 222 to beoperated and switch 243 positioned as illustrated, the ground potentialon wire PON is extended .to the battery-V connected winding of theprimary oft-normal relay 223.

Primary olf-normal relay 223 operates and at its .make contacts 2extends ground potential to the battery-.connected winding of relay 229,which operates and connects hold magnet operate wires H13/l1 to HM`12 torespective test conductors TE1 to T1512, and at its makebefore-breakcontacts extends ground potential through the brush of switch 243 andengaged bank contact to the battery-connected winding of the hold magnetHMI associated with the selected trunk 150. At the same time, its breakcontacts 2 remove ground potential from the release wire RLSE.

Hold magnet HMI operates and closes the crosspoints .Slrtstl bythe-ptiagipal and auxiliaryaelcct magnets and the hold magnet, therebyextending the connection from the calling line L1 to the selected idletrunk 150.

Responsive to the operation of hold magnet HM, its operating ground isfurther extended through its Oifnormal contacts to the sleeve conductorS of the associated trunk, such ground being extended rearwardly tooperate the cutoi relay of the calling line circuit, causing line relay1@ to restore and remove ground potential from the units-mark andtens-mark wires.

Responsive to the seizure of selector SELl, the operation of the usualhold relay therein grounds the sleeve conductor S to maintain the holdmagnet HMI and the cutoff relay 12 operated after the controller CRI isrestored, and removes idle-indicating battery potential from the sleeveas a current-saving operation.

At the time that relay 223 operates, its break contacts 2 remove groundpotential from the release conductor RLSE as noted, therebyopen-circuiting start relay 212 which due to the copper sleevesurrounding its core, is slow-restoring. After a slight delay, startrelay 212 restores to remove ground potential from the lock conductor Lthereby restoring units-test relay 215 and trunk-test relay 222,Responsive to the removal of ground from the unitsmark and tens-markwire by the restoration of line relay 19, the tens-group relay,tens-test relay, the operated select magnets, and the call-in relays arerestored, thereby returning the controller to common use.

In the event that the controller CRI fails to find an idle trunk withina predetermined time, slow-operating time relay 214 operates andopen-circuits the start relay 212 which restores to clear out thecontroller in the manner above described.

In the event that controller CRI and controller CRZ each receive a callfrom lines served by switch 1, the hereinbefore described operationtakes place giving select magnet call-in relay 217 of controller CRIpreference over the corresponding relay of controller CR2. In thismanner no interference between the common elements, such as the selectmagnets of switch 1 is encountered.

At such time, however, the tens switch, units switch, and trunk switchesof the waiting controller are positioned to identify the calling lineand to select an idle trunk irrespective of the operation of the selectmagnet call-in relay of the waiting controller. In this manner, thedelay time of the waiting call is minimized and when the switch becomeidle, as regards the waiting controller, the associated select magnetcall-in relay of the waiting controller operates to complete the switchhorizontal and vertical selection to extend the calling connection.

Time relay 214 is shown under direct control of start relay 212 butarrangements may be provided wherein the timing is discontinued in acontroller waiting for switch individualization so that a more criticaladjustment of the timing relay is possible, the timing then beginninganew responsive to the operation of the associated select magnet call-inrelay.

I claim:

l. In a switching lsystem for interconnecting lines and trunks, crossbarswitches each including two sections and having select magnets common toboth sections, each section including a set of horizontal multiplescorresponding respectively to the common select magnets Iand including aset of vertical multiples intersecting the associated horizontalmultiples, each section further including hold magnets and associatedcrosspoint means for connecting any horizontal multiple of the sectionto any vertical multiple thereof under the joint control of the holdmagnets of the section and the common select magnets, lines connected toone set of the multiples of any said section :and trunks connected tothe other set of the multiples thereof, whereby the crosspoint means ofany such section can interconnect any associated trunk with any desired`associated line, switch controllers associated with respective groupsof the said sections with each controller being `common to the sectionsof its associated group of sections, the sections of at least one switchlying in :separate groups and being assigned to separate switchcontrollers, rst means in any switch controller for temporarilyindividualizing that controller with any associated section, secondmeans in any switch controller for temporarily individualizing thatcontroller with the select magnets of the switch containing theindividualized section, each switch controller including means forselectively controlling the individualized common select magnets and thehold magnets of the individualized section to connect any desiredassociated trunk with any desired associated line, means in each of theswitch controllers which are associated with respective sections of thesame switch for insuring that not more than one switch controller canbecome eiiectively individualized with the select magnets of the sameswitch at the same time.

2. In a switching system according to claim 1, wherein a rst switchcontroller is associated with one section of each 'switch of a group ofswitches of which the other section of each is associated with anotherswitch controller, means contained in the said means for individualizingthe switch :controllers for permitting the said first switch controllerto become effectively individualized with its associated section andwith the `common select magnets of any switch of said group irrespectiveof the state of individualization as to any other switch of the groupand another switch controller.

3. In a switching system according to claim l, means included in thesaid individualizing means for permitting a switch controller to becomeindividualized with its associated section of a switch irrespective ofthe concurrent individualization of the select magnets of that switchwith another switch controller.

4. -In a switching system according to claim l, wherein the switches areline-finder switches with the lines connected -to respective horizontalmultiples and with the trunks connected to respective vertical multiplesof any section, means responsive to a calling condition on any line forcontrolling the said rst and second individualizing means of theassociated switch controler to indi- Vidualize that controller with thehold magnets of the switch section containing the calling line and withthe select magnets of that switch, means in the switch controller forSelecting the calling line and for selecting an idle trunk associatedwith the pertaining switch section, means in the switch controller foroperating the select magnet corresponding to the horizontal multipleconnected to the selected calling line, and for operating the holdmagnet associated with the selected idle trunk, to control thecorresponding crosspoint means to connect the selected trunk to theselected calling line.

5. In a switching system according to claim 4, wherein certain of thetrunks are connected to vertical multiples of separate sections whichmay be associated with separate switch controllers, temporary means inany controller for applying a first distinctive marking potential to aconductor of the selected trunk to mark such trunk unavailable to anyother controller before it has been connected to the calling line, andmeans responsive to the connection of the selected trunk to the callingline for substituting a second distinctive marking potential on the saidconductor.

References Cited in the rile of this patent UNITED STATES PATENTS2,674,657 Bellamy et al Apr. 6, 1954 2,683,773 Diesen July 13, 19542,686,841 Boyer c Aug. 17, 1954

